Right Trapezium - Simple Problem Using Trigonometry 1. The problem statement, all variables and given/known data http://img207.imageshack.us/img207/8510/imagejat.jpg [Broken] ABCD is a right trapezium. CB = 3 = CD. P is a point of CB. The angle CDP is called x. I have to express the function f(x) = DP + CP and I have to find the interval in which the function can be considered. 2. Relevant equations 3. The attempt at a solution I've found the function: http://img836.imageshack.us/img836/848/imageuox.jpg [Broken] But I can't understand how I can find the interval. Thank you very much for helping! PS: the solution on my book is 0<=x<=30º.